Burcell's zebras are a particular species of the plains zebra found in Africa.  They used to roam free across large portions of Africa but were thought to have been hunted to extinction in the early 20th century.  The last known Burchell's zebra in captivity died in Berlin in 1918.  But almost 100 years later they were found to still exist in protected areas in Etosha (Namibia) and Kwazulu-Natal (South Africa).  The reason they exist only in these protected areas is most likely because they weren't hunted to the verge of extinction, both for sport and for bush meat.  Also, humans have taken over former natural grazing areas.  These events have allowed small populations to survive in protected areas where they are left free to flourish in small, concentrated colonies.